1. Technical Field
The present invention relates to a nozzle plate, a discharge head, a method for producing the nozzle plate, a method for producing the discharge head, and a discharge device.
2. Related Art
As a droplet discharge head for discharging a droplet, an ink-jet head incorporated into an ink-jet head recording apparatus, for example, has been known. The ink-jet head generally includes a nozzle plate in which a plurality of nozzle holes for discharging ink drops are formed and a cavity plate bonded to the nozzle plate and having ink channels formed therein, the ink channels such as discharge chambers and reservoirs which are communicated with the nozzle holes between the cavity plate and the nozzle plate, and is configured to discharge an ink drop through a selected nozzle hole by applying pressure to the discharge chamber by a drive part. As driving means, there are a system using electrostatic force, a piezoelectric system based on a piezoelectric element, a bubble jet® system using a heater element, and the like.
In recent years, the demand for an ink-jet head with high print quality and high image quality has become stronger, and, to realize such an ink-jet head, there has been a growing demand for a denser ink-jet head and an increase in discharge performance. It is under this background that various efforts and suggestions have been made for a nozzle section of the ink-jet head.
To improve the ink discharge characteristic of the ink-jet head, it is desirable to adjust the channel resistance of the nozzle section and adjust the thickness of the substrate so as to provide an optimum nozzle length. When such a nozzle plate is produced, as shown in JP-A-11-28820 (Patent Document 1), for example, a method has been adopted by which a first concave portion (a concave portion which becomes a discharge port of the nozzle hole) and a second concave portion (a concave portion which becomes a feed port of the nozzle hole) for forming the nozzle section, the first concave portion and the second concave portion having different inside diameters, are formed in two stages by performing anisotropic dry etching using ICP (inductively coupled plasma) discharge from one surface of the silicon substrate, and then the length of the nozzle is adjusted by performing anisotropic wet etching on a part from the opposite surface (see, for example, Patent Document 1).
On the other hand, as shown in JP-A-9-57981 (Patent Document 2), for example, there is a method by which a discharge port and a feed port of the nozzle hole are formed by polishing a silicon substrate to an intended thickness in advance and then performing dry etching on both surfaces of the silicon substrate (see, for example, Patent Document 2).
However, as in Patent Document 1, when the discharge surface in which the nozzle hole opens is the bottom of the concave portion formed deeply one step down from the substrate front surface, a curved flight of an ink drop occurs, or, when paper powder, ink, or the like, which clogs the nozzle holes adheres to the bottom of the concave portion which is the discharge surface, it is difficult to perform wiping for wiping the bottom of the concave portion clean with a rubber piece or a felt piece to remove the paper powder, the ink, or the like.
Moreover, with the production method described in Patent Document 2, the thickness of the silicon nozzle plate substrate has to be made thinner as the ink-jet head becomes denser; however, such a silicon substrate is apt to splinter during a production process and becomes expensive. Furthermore, when dry etching is performed, cooling is performed from the back surface of the substrate by using He gas or the like to stabilize the work shape. In this case, it becomes sometimes impossible to perform etching due to a leakage of the He gas at the time of formation of the nozzle hole. It is for this reason that, as described in JP-A-2006-159661 (Patent Document 3), a method for producing a nozzle plate has been adopted by which concave portions which become nozzle holes are formed in a silicon substrate in advance, the substrate is bonded by using, for example, a double-faced sheet having a peel layer on one side of the bonding layer, the peel layer whose adhesion power is easily weakened by a stimulus such as ultraviolet radiation or heat, and then the nozzle holes (the concave portions) are formed by working the silicon substrate into a thin plate by grinding, CMP, or the like. In addition, an ink-repellent film is formed on the discharge surface, and primer treatment is performed on the adhesive surface to enhance the strength of adhesion to the cavity.
However, in this method for producing a nozzle plate, since the whole surface of the discharge surface is coated with the ink-repellent film, a head formation member (a cover head) protecting the periphery of the ink-jet head is bonded to the discharge surface with low bonding strength, reducing the reliability of the head.